It isn't that you doesn't have a plural form, but rather you *is* the plural form of itself. In most cases, I think the use of "you all" is just a result of poor grammar, and is often heard in more southern dialects. Although, in the sentence, "I am expecting answers from you all" I think it's ok, but in this case it is used to emphasize "*all* of you" instead of a more general plural "you".

The southernism is YA'LL (which spelling is the one usually insisted on by a southerner). A 2nd person plural is common in languages other than English, and it's not uncommon for English-speakers to adopt their own version of the 2ndpp to make up for its absence. Where southerners have YA'LL, others, including my fellow Liverpudlians, have YOUSE.

The proper spelling of the word, to the extent there is a proper spelling, is "y'all." "Y'all" is a contraction, like "don't" and "isn't." The apostrophe stands for the dropped letters "O" and "U."

"You" is either singular or plural, or usable when you don't know or don't want to specify singular or plural.

"Y'all" can sometimes be used in the singular, but I rarely hear the singular usage anymore, and I never hear it in Texas. It means the same thing as, and is interchangeable with, "you all" (depending on how slow your drawl is). It is plausible to me that sometimes "you all" in modern speech is actually a re-expanded "y'all."

"All y'all" is a "superplural" that you hear used in contexts like the following: "I can go with y'all in the car, or with y'all in the truck, but I can't go with all y'all at the same time." "All y'all kids get out of the mud and get some ice cream--it ain't waitin' on all y'all."

Oh, yeah, "you" and "all of you" is the way I learned it growing up, part of which I actually did in Michigan. I didn't pick up "y'all" until I moved to Texas (the first time) when I was 12.

Since the subject hasn't really been addressed, I'll point out that the word "you," far from having no plural, *is* the plural. The singular form, no longer used in standard English, is "thou" or "thee" (depending on its grammatical function).

I learned from the Quakers that at the time of their founding, around 200 years ago, both "you" and "thou" were used in the singular in standard English. The choice between them was made based on how close or familiar your relationship was with the person you were addressing. Since Quakers wished to emphasize the status of every person as a brother or sister in Christ (as they saw it), they used only the more familiar form. They continued to speak this way even when 'thou" fell out of standard usage. It's rare to find a modern Quaker who still does this, though.

Oh, yes, and it happens in Spanish too, with the "familiar" form "tu" and the "formal" form "usted" (plural, "ustedes"). Because the word endings of nouns that agree with "usted" resemble plural endings, I sometimes tease my Hispanic co-workers with this mock-innocent query:

"The Spanish word for 'day' is 'día,' right?"

"Yeah, right."

"And if you wanted to talk about more than one day, you'd say 'días,' right?

"Yeah, that's right."

"So when we tell someone 'Buenos días,' we're actually talking about more than one day, right?"

(Look of utter confusion on my friend's face as they try desperately to articulate a grammatical principle they've taken for granted since they began to talk. Heh.)

I grew up in Mississippi, and in all our notes to each other as students in school, it was ya'll. That's just the way everybody spelled it. Several years ago someone pointed out to me that this is incorrect, and I agree, because you put the apostrophe where you leave out the letters, as y (ou) 'all. However, I've spelled it wrong all my life, and at my age I reserve the right to continue to spell it that way. I bet all my classmates from Vicksburg are still spelling it wrong, too!

I think you all are forgetting something important: the fact that language changes. We do in fact have a second person plural in english, and it is formed by saying the word "you" with a modifier, for example, you all, you three, you people, etc. Please do not subscribe to the professor's english, so strict and unchanging, and instead recognize the fact that "proper" english is the way that english is actually spoken, not the way some grammar professor says you must speak it.